package com.sima.java.Singleton;

/**
 * Created by maple on 2017-08-19.
 */
public class Singleton {
    /* 持有私有静态实例，防止被引用，此处赋值为null，目的是实现延迟加载 */
    private static Singleton instance = null;

    /* 私有构造方法，防止被实例化 */
    private Singleton(){

    }

    /* 静态工程方法，创建实例 */
    /*
    public static Singleton getInstance(){
        if (instance == null){
            instance = new Singleton();
        }
        return instance;
    }
    */
    /*
    public static synchronized Singleton getInstance(){
        if (instance == null){
            instance = new Singleton();
        }
        return instance;
    }
    */
    /*
    public static Singleton getInstance(){
        if (instance == null){
            synchronized (instance){
                if (instance == null){
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
    */

    private static class SingletonFactory{
        private static Singleton instance = new Singleton();
    }
    public static Singleton getInstance(){
        return SingletonFactory.instance;
    }

    /* 如果该对象被用于序列化，可以保证对象在序列化前后保持一致 */
    public Object readResolve(){
        return instance;
    }
}
